Optical communications afford a highly efficient method of information transmission, particularly in high speed digital and analog transmission of information. The emergence of active optoelectronic devices heighten this efficient method of data transmission. There are attendant difficulties in effecting lightwave communications, not the least of which is inefficient coupling of a waveguide to an active device.
One source of inefficient coupling is misalignment of the fiber to the device. The emergence of silicon waferboard technology has provided means to accurately align optical fibers in a passive manner. As disclosed for example in U.S. Pat. Nos. 5,224,784; 5,163,108; 5,077,878 and 5,182,782, by etching along preferred crystallographic planes in a silicon waferboard, "V" grooves are formed for accurate passive alignment of optical fibers with active devices and or coupling fibers. One example of the use of crystallographic planes in the alignment of an optoelectronic device to a fiber using a silicon substrate is disclosed in U.S. Pat. No. 4,210,923 to North, et al. In '923, an SiO.sub.2 mask is applied to a silicon substrate having a major surface in the (110) crystal orientation. By application of KOH solution and water, anisotropic etching is achieved and V grooves are formed with sidewalls in the (111) crystalline planes. As further discussed in North, et al. the precise depth of the V groove can be made by picking the requisite width of the groove. Thereby, due to the known characteristic relative angles of the crystallographic planes, the accurate passive alignment of the optical fiber to the optoelectronic device is achieved. An electro-optic detector is grown on the substrate via conventional methods and light from the fiber is coupled to the edge receiving detector. North, et al. has no provision for focusing the incoming light from the fiber to the active device. Accordingly, there are attendant problems with back-reflections as well as inadequate coupling of the light due to this inability to properly focus. Other examples of masking and etching monocrystalline silicon to reveal, at desired locations grooves and/or apertures with side walls in preferred crystallographic planes are disclosed in U.S. Pat. Nos. 4,897,711; 4,779,946 and 4,466,696, incorporated herein by reference. These references disclose the use of various etching techniques to create alignment grooves to increase the coupling efficiency of light between optical fibers and between a fiber and a device.
In U.S. Pat. No. 4,897,711, the use of a focusing member is disclosed. In this reference, a top emitting LED is mounted on a substrate. A second piece of silicon is etched and a reflecting surface formed thereon to couple light from the LED to a fiber mounted in a V groove. A lens is mounted in an anisotropically etched pyramidal hole in an intermediate silicon piece to focus the light from the LED to the fiber. U.S. Pat. No. 5,073,003 teaches a structure similar to the '711 patent but further aligns the LED by crystallographic etching to effect coupling of light to the fiber with approximately a zero degree angle of incidence. U.S. Pat. No. 5,224,184 to Boudreau describes the use of a waferboard substrate which has mounted thereon a semiconductor device, a planar optical waveguide and a focusing element therebetween. The focusing element in this case is a geometrical or GRIN lens which is placed in a relief (to include a "V" shaped cavity) in the substrate and focuses light between the device and the waveguide. The lens has mounted thereon a handle for aligning the lens to properly focus between transmit and receive ports. Thereby the positioning of the lens requires active alignment between optical ports. After alignment the lens is secured by various techniques including soldering and welding. Finally, U.S. Pat. No. 5,123,073 to Pimpinella describes the use of inverted pyramid-shaped wells which hold lens spheres that effect focusing between coaxially aligned fibers set in "v" grooves. The invention requires the use of a two part housing and cylinders for mechanical alignment.
It is desirable to be able to accurately couple light between an optoelectronic device and a fiber with high coupling efficiency and thereby high signal power transfer. To this end, it is an object of this invention to be able to provide a high precision, efficient optical interconnection between fibers and optical devices by passive alignment of a focusing element. This passive alignment is achieved with great accuracy by employing the characteristic crystalline planes of crystalline materials such as silicon in both the substrate and the substrate that forms the focusing element.